The invention relates both to a method and to a use by this method of an apparatus for detecting blocking of a direct current motor, in particular a direct current motor for a blower of a motor vehicle.
From German Patent Disclosure DE-A 40 40 847, a method for monitoring and triggering an electronically commutated direct current motor is known, in which the running of the motor is monitored by measuring, via a measuring resistor, a frequency and/or a voltage that corresponds to either the current picked up by the motor or the frequency. In the event of blocking or nonstandard running of the motor, an error signal is generated, which indicates an overshooting or undershooting of predetermined limit values on the part of the measured frequency or voltage. In order to achieve motor startup with high certainty even in the event of a tendency to blocking or with starting errors on the part of the motor, the motor is repeatedly switched off and on again if an error signal is present.
From European Patent Disclosure EP-A 0 518 538, a regulating system for an electrically commutated direct current motor of a breathing device is also known, with which the speed of the motor is monitored on the basis of the induced voltage (back EMF) generated by the motor. To that purpose, it is provided that the voltage supply to the motor be briefly interrupted at intervals. Moreover, the current of the motor is also monitored, by means of the voltage that drops across a resistor connected in series with the motor. From the monitored signals, a virtually constant flow of the breathing air can be assured by the regulating system even in the event of increasing blocking of the flow rate as a consequence of clogging air filters.